General thermoplastic synthetic fibers such as nylon or polyester fibers commonly used for clothing and industrial materials melt at about 250° C., have a limiting oxygen index of about 20, and thus burn well in the air. Accordingly, these general thermoplastic synthetic fibers are not considered suitable as protective fiber raw materials for clothing products used in a situation where they have a high risk of being exposed to flames and high temperature, including firefighting clothing, racing suits for motor races, workwear for steel industry workers or welders, and gloves.
Heat-resistant high functional filament yarns, such as aramid fibers, wholly aromatic polyester fibers, and polyparaphenylene benzobisoxazole fibers, do not melt at about 250° C. and has a decomposition temperature as high as 400° C. or more. These yarns have a limiting oxygen index of about 25 or more, and burn in the air when a flame, which is a heat source, is brought close thereto but the inflammation does not continue when the flame is moved away.
Thus, heat-resistant high functional filament yarns are materials having excellent heat resistance and flame retardancy. For this reason, for example, aramid fibers, which are heat-resistant high functional filament yarns, are preferably used for clothing products worn in a situation where they have a high risk of being exposed to flames and high temperature, for example, in the form of protective clothing such as firefighting clothing, racing suits for motor races, workwear for steel industry workers or welders, and gloves. Of these yarns, para-aramid fibers having both heat resistance and high strength properties are used for sportswear, workwear, ropes, tire cords, and the like, which require tear strength and heat resistance, and also used for wound protection work gloves and the like because of their knife-cutting resistance.
As para-aramid fibers, polyparaphenylene terephthalamide (PPTA) fibers are well known, and methods for producing PPTA fibers are disclosed in, for example, U.S. Pat. No. 3,767,756 and Japanese Patent Publication No. 56-128312. On the other hand, meta-aramid fibers, unlike para-aramid fibers, do not have cut wound resistance or high tensile strength, but are used for firefighting clothing, heat insulation filters, heat-resistant dust filters, electrical insulation materials, and the like, because of their heat-resistance properties.
Conventionally, when manufacturing clothing products using these heat-resistant high functional filament yarns, these fibers were only used in the form of non-stretch filament yarns or spun yarns. However, when non-stretch yarns such as filament yarns or spun yarns are processed into a fabric to produce clothing products such as firefighting clothing, racing suits or workwear, the obtained clothing products have poor stretchiness and poses the disadvantages of being uncomfortable and making it difficult to move when the clothing products are worn. Conventional work gloves similarly made of non-stretch yarns also had a sense of ill-fitting, causing work efficiency to be reduced.
Considering the demand in the related markets, many studies and proposals on a method for imparting a crimp to heat-resistant high functional filament yarns have been conducted. For example, known methods include a method in which a low modulus fiber is mixed into a high modulus fiber such as a para-aramid fiber and a crimp is imparted by a stuffing box method (Patent Literature 1), a method in which an aramid fiber is subjected to false twist crimping using a non-contact heater heated to a decomposition initiation temperature or more and less than a decomposition temperature thereof (390° C. or more and less than 460° C. for meta-aramid fibers), followed by relaxation heat treatment to impart a crimp (Patent Literature 2), and a method in which a heat-resistant high functional fiber yarn such as para-aramid fibers is twisted and then heat-set by hydrothermal treatment at 130 to 250° C. or dry heat treatment at 140 to 390° C. and subsequently untwisted (Patent Literature 3).
It is also reported that protective gloves or the like having excellent burn resistance, heat resistance and stretchability are obtained by composing a woven or knitted fabric using a covered yarn prepared by winding a spun yarn or a crimped yarn of a para-aramid fiber around a stretchable elastic fiber (Patent Literatures 4 to 6).
Patent Literatures 5 and 6 disclose a crimped yarn of a para-aramid fiber having a stretch recovery ratio ranging from 4 to 80%. Specifically, Patent Literature 5 discloses that a twisted yarn is subjected to high temperature high pressure water vapor or high temperature high pressure water treatment at 130 to 250° C. (so-called wet-heat treatment) or by dry heat treatment wherein the yarn is heated in the air, to set the twist, and the twisted yarn with the twist fixed is untwisted in the opposite direction to the above direction to obtain a crimped yarn. Accordingly, in Example 1, a twisted para-aramid fiber is treated with saturated water vapor at 200° C. for 15 minutes to set the twist and subsequently untwisted to obtain a crimped yarn having a shrinkage/elongation ratio of 29.0% and a stretch recovery ratio of 8.2%, and in Example 4, a twisted para-aramid fiber is subjected to dry heat treatment at 100° C. for 30 minutes to set the twist and subsequently untwisted to obtain a crimped yarn having a shrinkage/elongation ratio of 29.0% and a stretch recovery ratio of 8.0%.
Patent Literature 6 discloses that a glove which was knitted using a covered yarn obtained by winding the crimped yarn of a para-aramid fiber obtained in Example 1 of Patent Literature 5 around an elastic fiber and coated with a urethane resin was stretchy, fitted a hand well and enhanced workability.
The protective gloves and the like have at least a part of the back and palm sides of the glove coated with a rubber or resin coating material to impart reinforcement and waterproofing properties; however, a problem of the protective gloves obtained in Patent Literature 6 is that they have poor adhesiveness between the coating material and the glove material, which causes the coating material to peel off while using the gloves, thus failing to provide durable gloves.
Another problem is that when the amount of the coating material adhered is increased for the purpose of enhancing the adhesiveness and durability of the coating, the gloves do not fit well and adversely affect workability when worn and the degree of freedom of monofilaments is reduced because the coating material firmly binds the high strength fiber, causing reduced cut wound resistance.